A green, red, black, and white 3-D image of a patient's entire body rotates on a computer screen before Gordon Harris and Wenli Cai. Harris points out a number of tumors, hallmarks of a genetic disease called ­neurofibromatosis (NF). ­Harris's research group at Massachusetts ­General ­Hospital, where he is director of 3-D-imaging services, is preparing a clinical trial to test a technique for monitoring patients, like this one, affected by NF. The technique combines PET imaging and a relatively new imaging technology called whole-body MRI. [Disclaimer: Jason Pontin, the editor in chief and publisher of Technology Review, serves on the board of directors of the Children's Tumor Foundation, which awarded a grant to Harris for the research described here.]

Most people have never heard of ­neurofibromatosis, though its three forms affect over 100,000 Americans--more than suffer from cystic fibrosis, Huntington's disease, and Tay-Sachs disease combined. About one in 3,500 babies worldwide is born with the most common form, NF1. NF1 patients may have noncancerous tumors growing along the nerves and on the skin of any part of the body. These tumors can cause pain and disfigurement; more rarely, they turn cancerous.